TBR: i#95 Linux detach: generalize call_switch_stack

Commit log for first patchset:
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i#95 Linux detach: generalize call_switch_stack

Generalizes call_switch_stack() to take any void * argument to its target
function: it does not need to be a dcontext_t.  This is in preparation of
using other types for detach code.
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[bruening, 2016-09-13 22:30:51]

Committed as
https://github.com/DynamoRIO/dynamorio/commit/c7524accde0f558f3f745b2e6fed8d7...

Final commit log: 
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i#95 Linux detach: generalize call_switch_stack

Generalizes call_switch_stack() to take any void * argument to its target
function: it does not need to be a dcontext_t.  This is in preparation of
using other types for detach code.

Review-URL: https://codereview.appspot.com/303560043
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